1. FIELD OF THE INVENTION
The invention relates to a method and apparatus for effecting the injection of steam at a selected mass flow rate into one or more production formations traversed by a subterranean well.
2. HISTORY OF THE PRIOR ART
Injection of high-temperature steam into production formations of subterranean wells has been a common practice, particularly where the hydrocarbons contained in the production formation is highly viscous. A typical subterranean well normally traverses more than one production formation, which may be spaced apart by thousands of feet in the well. The steam injected into each production formation must obviously be at a pressure in excess of the formation pressure and at a temperature and mass flow rate high enough to effect the desired reduction in viscosity of the hydrocarbons contained in the particular production formation.
With conventional apparatus, the amount of pressure required to introduce steam at a desired flow rate and temperature to each of a plurality of vertically spaced production formations has required that the steam generator located at the surface produce steam at high pressures; and the higher the pressure, the greater the cost of the apparatus for production of such steam, and the operating cost.
This objective has not been efficiently accomplished in the prior art systems. It has been the practice when injecting steam into multiple formations to run multiple lengths of tubing string so that each string supplies steam to a separate formation. Obviously the cost of installing and operating such steam injection system is excessive. The industry needs a single tubing system for supplying selected quantities of high-pressure steam simultaneously and economically to a plurality of vertically spaced production formations in a well.